The present invention provides a method and apparatus for projecting ultraviolet light through man-made energy and illumination sources. More particularly, the present method and apparatus provide for skin tanning through the use of a plurality of ultraviolet light emitting diodes (LED""s) in combination with a power modulation circuit.
All human beings need and crave sunlight. In particular, virtually everybody desires the warm and pleasant sensation associated with sunlight. One desired side effect of exposure to strong sunlight is the xe2x80x9ctanningxe2x80x9d effect upon human skin. Tanning occurs when the skin produces additional pigment (coloring) to protect itself against burning from ultraviolet radiation (UVR) present within sunlight. Ultraviolet radiation, sometimes also called ultraviolet light, is invisible electromagnetic radiation of the same nature as visible light, but having shorter wavelengths and higher energies.
When strong, naturally occurring sunlight is not obtainable, projecting man-made UV light upon human skin is a desirable substitute. xe2x80x9cTannedxe2x80x9d skin is generally considered physically attractive, and a large market exists to serve people with artificially generated UV lighting systems that will provide a tanning effect in the absence of natural sunlight. Other benefits associated with the reception of UV radiation is the production of vitamin D by the skin; and the prevention of depression and other xe2x80x9cseasonal affective disordersxe2x80x9d (SAD""s) during the dark winter months in locations distant from the equator. Accordingly, millions of people seek ways to enjoy ultraviolet light and, in particular, to keep their skin tanned, in the absence of naturally occurring strong sunlight.
Prior art tanning xe2x80x9cbedsxe2x80x9d and xe2x80x9cboothsxe2x80x9d are well-known, popular devices that utilize rows of fluorescent lighting tubes to project UVR upon a person in order to cause the person""s skin to tan. These are particularly popular in northern regions of the United States, where strong sunlight is not available during the fall and winter months. A typical prior art fluorescent lighting tube tanning bed or booth forms an enclosure about a person being tanned. Once inside the prior art bed or booth, a person is surrounded by a plurality of fluorescent tubes arranged in rows or other configurations that are intended to directly or indirectly illuminate a person""s exposed skin.
The use of UVR fluorescent tubes has a number of significant disadvantages. They have large power requirements, resulting in high energy costs for systems utilizing them. They also emit large amounts of heat, resulting in needless heat exposure for UVR fluorescent tube system users.
It is also preferable to keep the distance between the skin and each of the plurality of tubes within a more or less common range. Otherwise, skin that is closer to the fluorescent tubes will receive more UVR and, thus, tan or suffer erythema (burn) quicker than skin positioned farther away. Designing tanning beds or booths of fluorescent lighting tubes that assure a uniform distance between a person""s skin and the fluorescent tubes is problematic. The arrangement of fluorescent tubes is generally restricted by the long linear shape of the fluorescent tubes. Since body shapes are not linear, a person aligned more or less parallel to a bank of fluorescent tubes will necessarily have some skin regions much closer to the tubes (for example, the tip of the nose) than others (such as the intersection of the bottom of the neck in the top of the chest).
Moreover, in order to avoid undesirable gaps in illumination projection, generally the fluorescent tubes must be as long as the person receiving illumination. Therefore, the selection of UVR fluorescent tubes for the typical prior art tanning bed or booth is generally limited to long tubes arranged in rows. This results in large inefficiencies in energy utilization and fluorescent lighting requirements, wherein generally rectangular regions much larger than the general human profile must be illuminated by the fluorescent tubes.
UVR fluorescent lighting tubes also present problems with providing a consistent energy output profile. The typical fluorescent lighting tube is designed to emit a uniform and predictable amount of UVR. As the lighting tube ages, the amount of UVR emitted starts dropping off and, therefore, the effective tanning produced drops off. This UVR output drop-off is not apparent to an operator of the tanning bed or booth, or to a person using the tanning bed or booth, unless it is observed through less effective tanning or longer illumination times required to achieve the same relative tanning effect. Therefore, tanning booth or bed operators must keep track of the hours of service of a UVR fluorescent tube, and regularly replace the tubes at the end of a predicted service-hour life. As a result, perfectly good UVR fluorescent tubes are needlessly discarded, resulting in a huge and costly inefficiency throughout the UV tanning industry.
It has also become recently known in the tanning industry that the type of UV light is very important. In the electromagnetic spectrum, UVR extends between the blue end of the visible spectrum and low-energy X-rays, straddling the boundary between ionizing and non-ionizing radiation (which is conventionally set at 100 nm). Ionizing radiation, such as X-rays and gamma-rays, have enough energy to ionize (i.e. break up) atoms. Non-Ionizing radiation, such as visible light, microwaves, or radio waves, do not.
The frequency of electromagnetic fields is measured in Hz (hertz), or cycles per second, where 1 kHz (kilohertz)=1000 cycles/second. UVR is conventionally divided into three bands in order of increasing energy: UVA, UVB and UVC. This division corresponds broadly to the effects of UVR on biological tissue. The wavelength ranges in nanometers and common names of the UVR bands are:
UVA: 315-400 nm xe2x80x9cBlack lightxe2x80x9d
UVB: 280-315 nm xe2x80x9cErythemal UVxe2x80x9d
UVC: 100-280 nm xe2x80x9cGermicidal UVxe2x80x9d
Due to their different wavelengths and energies, each of these bands has distinct effects on living tissue. The highest energy band, UVC, can damage DNA and other molecules and is often used as a germicidal agent. UVC is rapidly attenuated in air and, therefore, it is not found in ground-level solar radiation. Exposure to UVC, however, can take place close to sources, such as welding arcs or germicidal lamps. UVB is the most effective UV band in causing tanning and sunburn (erythema) and it can affect the immune system. Although UVA is the least energetic UV band, and much less effective than UVB in causing erythema and tanning, it can cause these effects at levels present out-of-doors. UVA penetrates deeper in the skin due to its longer wavelength and plays a role in skin photoaging. UVA can also affect the immune system.
Because of a large difference in the efficiency of each UVR wavelength in causing biological damage, UVR exposure and dose are computed as weighted values. Each wavelength is assigned a weight according to its effectiveness in producing erythema or keratoconjunctivitis. The exposure thus calculated is called xe2x80x9ceffective irradiancexe2x80x9d and the dose, xe2x80x9cbiologically effective dose.xe2x80x9d
The main source of natural ultraviolet radiation is the sun. Most of the solar radiation reaching the surface of the earth is infrared radiation (55%) and visible light (40%). Approximately 5% of the ground-level solar radiation is ultraviolet radiation, mostly in the UVA range. Solar UVR varies strongly with season, time of day, latitude and atmospheric conditions, generally reaching a daily peak around solar noon and a yearly peak in summer. UVB levels change rapidly with time of day while UVA levels vary more slowly throughout the day. UVB is strongly absorbed by stratospheric ozone, so depletion of this protective layer results in higher UVB intensity at ground level. Exposure to solar radiation at noon in mid-latitudes, during spring and summer, routinely exceeds the threshold for damage to the eyes and skin within a few minutes.
In addition to solar UVR, which represents the main exposure to UVR for the majority of the population, there are a variety of artificial sources of UVR. Electric welding arcs are strong sources of ultraviolet radiation, and can produce acute overexposure to UVR within a radius of several meters in just a few seconds. Arc lamps, used in some specialized projection and illumination, and in the printing industry, can also be strong sources of ultraviolet radiation. Curing lamps use UVR to harden resins and to dry paints and other substances; they can be quite intense, and are usually located inside enclosed cabinets. xe2x80x9cBlack lightsxe2x80x9d are UVA lamps used for non-destructive testing, insect control, and in the entertainment industry. Germicidal lamps, commonly used for sterilization in hospitals, are strong emitters of UVB and UVC radiation. Therapeutic UVR lamps, used in physiotherapy and dermatology for the treatment of psoriasis and other skin conditions, can emit either UVA or UVB.
Studies suggest that children and adolescents may be tanned or burned more by equivalent amounts of UVB rays than adults. Common sunscreens are designed to filter out UVB rays. In contrast, longwave UVA rays do not greatly impact the outer skin layers and are less likely to cause burning than UVB rays. By penetrating deeper into skin layers and still generating a tanning effect, without burning or damaging the upper skin layers, UVA rays are considered by many to be a safer alternative to UVB rays. Accordingly, the typical prior art UVR tanning systems emit mostly UVA radiation with a few percent content of UVB, and their use can lead to significant exposures to UVA radiation. However, while UVA is less effective than UVB in causing erythema, it penetrates deeper in the skin, contributing to premature aging and other health effects, including carcinogenesis.
Moreover, the reaction of any one person""s skin to either type of UV lighting system is dependent upon the person""s skin type. In general, people with darker skin complexions can receive more UVB light without burning or suffering upper skin layer damage. Such a person may prefer UVB light over UVA light for its more rapid and, therefore, more time-efficient tanning effect. In contrast, people with extremely fair skin complexions may burn readily from even limited UVB exposure, and may not be able to effectively tan at all. They may wish to utilize only UVA lighting for other beneficial health effects. The majority of people using UV lighting systems will fall between these two extremes. Accordingly, each person may benefit from an individualized relative percentage UVA to UVB light rays, received over their own individual optimal exposure time frames. Prior art UVR fluorescent lighting systems typically emit only one constant UVA/UVB profile. The relative relation of UVA to UVB cannot be varied and still project an effective composite tanning UVR.
What is needed is a new and improved artificial UV lighting system and method that provides a means for more uniformly illuminating the human body, wherein the artificial lights used maintain a generally uniform distance from all of the exposed skin and, therefore, all of this exposed skin may receive the same relative UV lighting strength. What is also needed is a way to more efficiently conform the yield of the light illumination sources to the shape of the human body. What is also needed is a way to efficiently provide a reliable and predictable UV illumination output, one that does not require needlessly disposing of expensive lighting sources. Is also desirable to provide a method and system wherein the type of UV radiation may be selected; for example, wherein UVA, UVB, or other light radiation spectrums, or a blend of any of these spectrums may be selected and, more preferably, where the relative percentages a UVA and UVB and/or their relative intensities may be varied over time, dependent upon an individual""s needs.
A light emitting diode projection apparatus and method is provided for irradiating a subject with ultraviolet radiation, comprising a plurality of light emitting diodes configured to emit ultraviolet radiation and arranged in a matrix, and a power modulation control unit in communication with the diodes. The power modulation control unit is configured to energize and cause the diodes to emit light and thereby irradiate the subject with ultraviolet radiation sufficient to cause material physical change in the subject. In one embodiment of the invention the material physical change is skin tanning. The amount, intensity, duration and type of UVR projected by the plurality of UV LED""s may be varied by the power modulation control unit responsive to information input into the power modulation control unit.